The present invention is directed to a gear machining process wherein a rotating gear-like or worm-shaped tool is radially moved into engagement with a gear-type workpiece with the shape of the teeth of the tool and workpiece being such as to prevent engagement of said teeth until a subsequent relative circular feed movement is performed in opposite directions to machine first one flank of the workpiece teeth and then the other flank thereof.
In known processes of continuous gear machining by means of immersion scraping, immersion grinding and immersion honing of cylindrical spur gears, the workpiece is engaged with a gear-like, rotatably driven scraping or honing tool having a globoidal or hyperboloidlike shape in such a way that the desired gear geometry is obtained on the workpiece with a radial advance movement between the tool and the workpiece when the distance of the axes of the tool and the workpiece, which are crossed towards each other, has reached the final value or the desired distance between axes which corresponds to the profiles of the tool and those of the finished machined workpiece.
An advantage of this process, for example, in comparison with the well known continuous gear rolling grinding with a cylindrical grinding worm, is seen in the fact that the desired workpiece geometry can be produced by a single movement between tool and workpiece, i.e. the immersion feed, since the line of engagement between the tool and the workpiece extends across the entire width of the workpiece when the rated axis distance (desired distance between axes) is reached and that a high material removing capacity can be reached due to the great length of the engagement with the workpiece. Since an additional axial machining feed is thereby eliminated, the process is very economical. Such a known process, as described above is covered by the German Disclosure Publication No. 25 16 059 which discloses the use of a rotating, gear-like tool for the production or machining, particularly for the grinding, of the teeth of straight or oblique spur gears. The tool consists of a grinding worm in the described embodiment.
As is generally known, no definition-bound difference is made between a gear and a worm in gear technology. The latter represents, in the technical sense, an oblique gear which may have a small number of teeth, even one. For this reason, the term "gear-like tool" comprises worms as well as other gears which may have teeth inside and outside. The machining can be effected through chipping, removing and also reshaping.
The prerequisite for the grinding with only one radial advance movement is the covering of the teeth of the tool with those of the workpiece, i.e. the joint tooth engagement must extend from the one face of the workpiece to the other whereby the tool has a hyperboloid or globoidal-like shape. The tool, in this instance the grinding worm, must be circumferentially shaped in such a manner that it forms a correct tooth engagement with the teeth of the workpiece when the rated production axis distance is reached. In case of tooth corrections, the tool must be provided with these corrections, for example, corrections for tip relief profile ease-off and base relief profile ease-off.
The machining of the workpiece according to the known process of pure cutting-in has a number of disadvantages. At the beginning of the machining, the workpiece has a more or less large dimension which is to be machined, i.e. there is a deviation between the real shape of the workpiece and the shape which the workpiece will have at the end of the immersion machining and to which the tool shape is coordinated.
This discrepancy between tool and workpiece shape, which will only disappear with the removal of the undesired portions of the workpiece, i.e. when the machining process is terminated, has the effect that, at the beginning of the machining, very unfavorable engagement conditions with unsymmetrical, point-shaped engagements exist depending on the height of the workpiece to be machined which run counter to a high material removing capacity. This means that this process is only superior to other processes with workpieces having a relatively small amount to be machined which requires a correspondingly high precision of the preliminary machining.
Furthermore, the non-uniform material removal leads to undesirable burned spots with a fast feed. This is particularly true because the cooling is insufficient between the tool and the workpiece upon immersion since the teeth of the tool fully fill the tooth gaps of the workpiece and there is no space for the cooling agent.